PROJECT SUMMARY Churning, or frequent gaps or transitions in coverage, is a persistent and harmful problem that is associated with poor access to care and higher rates of potentially preventable healthcare utilization. Medicaid expansion under the Affordable Care Act (ACA) has the potential to promote stability of coverage and reduce adverse healthcare utilization among low-income Medicaid beneficiaries. However, while recent evidence has identified a reduction in the uninsured rate, there is limited empirical work assessing the impact of expansion on coverage stability and healthcare utilization. The long-term goal of this research is to identify policies that improve access to care for low-income Americans. The immediate objective in this proposal is to evaluate how Medicaid coverage expansions impact continuity of health insurance coverage and healthcare utilization. We hypothesize that coverage expansions will improve enrollee retention in Medicaid, reduce emergency department visits and ambulatory-care-sensitive hospital admissions, and increase outpatient visits. Guided by preliminary data, the specific aims of this proposal are to: (1) Assess the impact of Medicaid expansion under the ACA on continuity of Medicaid coverage, and (2) Evaluate the impact of Medicaid expansion on the rate of outpatient visits and potentially preventable acute care utilization. Our sample includes non-elderly adults enrolled in Medicaid in 2013 in Colorado and Utah, who will be followed longitudinally through 2015. Examining Medicaid beneficiaries enrolled prior to expansion focuses on the enrollment groups who are most likely to benefit from eligibility expansions and who comprise the majority of the post-expansion Medicaid population. Both aims utilize a quasi-experimental econometric design that compares the outcome of interest among Medicaid beneficiaries living in a state that expanded Medicaid (Colorado), to a weighted control group of Medicaid beneficiaries living in a bordering state that did not expand Medicaid (Utah), pre and post Medicaid expansion. This approach is innovative because it takes advantage of state-based All Payer Claims Databases (APCDs) which include inpatient, outpatient, and prescription drug claims for nearly all health insurance payers, enabling us to identify whether Medicaid disenrollees transition to other sources of insurance. Previous analyses of Medicaid churning have been limited by the availability of central claims databases or by the representativeness and/or completeness of survey-based data at the state level. This proposal is the first post-ACA analysis to use such a database to measure continuity of coverage and utilization. The proposed research is significant because continuous access to care is the primary way Medicaid expansion can improve the health of low-income Americans. The expected outcome is a rigorous assessment of how Medicaid expansion influences insurance stability and healthcare utilization within the Medicaid program. While conclusions will pertain to the policy environments of the two states in the analysis, the findings will have important implications for other states considering expansion.